1. Field of the Invention
The present invention relates to a release sheet for the production of a matte synthetic leather and a composition for the formation of the sheet. More particularly, the present invention relates to a composition for matte layer formation suitable for the production of a matte synthetic leather, which has a matte surface with a high level of jet-blackness without the practice of embossing, raising or the like, and a release sheet for the production of a matte synthetic leather using the composition.
2. Prior Art
According to one of conventional production processes of synthetic leathers, a synthetic leather is produced by coating a composition for a synthetic leather, for example, a urethane resin, a vinyl chloride resin, a polyamide resin, or an amino acid resin, on a release sheet, drying or curing the synthetic leather coating, coating an adhesive onto the dried or cured coating, laminating a backing fabric, such as a woven fabric, onto the adhesive coating, and then separating the release sheet from the synthetic leather composition coating. In this production process of a synthetic leather, synthetic leathers having various surface shapes can be produced by regulating the surface form of the release sheet. Specifically, since the surface shape of the synthetic leather is formed by transferring the surface form of the release sheet onto the synthetic leather, the regulation of the surface form of the release sheet is necessary for the production of a desired synthetic leather.
One property required of synthetic leathers, particularly matte synthetic leathers, is freedom from a faded color and is to be jet-black, that is, is to be matte.
For example, the following methods are known for the production of these matte synthetic leathers. Specifically, in a conventional method, a release sheet having concaves and convexes on its surface is produced, for example, by utilizing an emboss roll as a chill roll in the step of extrusion lamination in the production of the release sheet or by utilizing an emboss roll as a chill roll in the step of forming an application film in the case of the formation of the release sheet by the application of an existing film, and the concave/convex shape of the surface of the release sheet is transferred onto a synthetic leather. In another conventional method, a release sheet with an emboss of concaves and convexes is prepared by embossing the whole release sheet, and the concave/convex shape of the surface of the release sheet is transferred onto a synthetic leather. In a further conventional method, a synthetic leather having a matte surface is produced by subjecting a synthetic leather to raising.
The synthetic leathers produced by these methods are suitably matte. Since, however, the shape of fine concaves and convexes cannot be imparted by the embossing and the like, satisfactory jet-blackness cannot be realized in synthetic leathers having a deep color, for example, a black color. Further, in the methods wherein raising or the like is carried out, a step should be additionally provided. This renders the production process complicate and incurs increased cost.
On the other hand, as described in Japanese Patent Laid-Open No. 158249/1985, a method for producing a matte synthetic leather, i.e., the so-called “synthetic leather with a matte tone,” has been developed wherein a composition for a release sheet with an inorganic pigment, such as silica or calcium carbonate, or a matting wax as a matting agent added thereto is coated onto a substrate to form a release sheet.
In the release sheet formed by coating the composition with a matting agent added thereto, however, the addition of a predetermined amount of an inorganic pigment or the like to the composition is necessary for attaining satisfactory matte effect. However, when the amount of this additive added to the composition is excessively large, the so-called “drop of particles” wherein the matting agent is dropped from the release sheet takes place.
Further, increasing the amount of the matting agent added for improving the matte effect causes aggregation of matting agent particles, and the matting agent disadvantageously bleeds out on the surface of the release sheet. Therefore, a release sheet having desired fine concaves and convexes cannot be formed, and, further, a synthetic leather, which is matte and is jet-black, cannot be produced.
Further, in the composition, for a release sheet, containing fine particles for matting purposes described in Japanese Patent Laid-Open No. 158249/1985 noted above, the incorporation of the fine particles can impart a matte feel to some extent. However, it is difficult to provide a synthetic leather which is jet-black without color fading.
The production of a matte synthetic leather by the conventional methods involves, besides the above problems, an additional problem that the addition of fine particles, which should be used as a matting agent for the production of a matte synthetic leather, to the composition for a release sheet deteriorates the fluidity of the composition and thus deteriorates the coatability of the composition.
Further, coating of a coating liquid onto a substrate having low smoothness to form a release sheet poses problems of deteriorated drying properties and lowered smoothness of the release sheet due to drying by strong heating.
When conventional paper is used as the substrate, static electricity is likely to be generated at the time of the formation of a release sheet. Further, in the production of a synthetic leather using this release sheet, since the step of separating the synthetic leather from the release sheet should be provided, the generation of static electricity is unavoidable. Thus, the generation of static electricity, for example, at the time of the production of a release sheet poses a problem of cracking of the surface of the release sheet and the synthetic leather.
Accordingly, an object of the present invention is to provide a composition for matte layer formation suitable for the production of a matte synthetic leather, which has a matte surface with a high level of jet-blackness without the practice of embossing, raising or the like, and a release sheet for the production of a matte synthetic leather using the composition.
Another object of the present invention is to provide a release sheet for the production of a matte synthetic leather, which release sheet has excellent smoothness and can realize the production of a good synthetic leather free from defects such as cracking by virtue of the suppression of the generation of static electricity.